This invention relates to guardrails intended to be positioned along a highway to reduce injury to the driver and passenger of vehicles that may accidentally tend to leave the highway.
In one class of guardrail system, each guardrail system includes an elongated barrier and at least one energy-absorbing terminal. The elongated barrier extends parallel to the roadway along the side of the roadway and ends in a terminal. The terminal cooperates with one or more components of the barrier to absorb energy when a vehicle hits the terminal itself.
The terminal is constructed to stop the vehicle without subjecting the occupant to excessive forces and to avoid impaling the passenger compartment of the vehicle or redirecting the vehicle in a dangerous direction or permitting the vehicle to continue in a dangerous direction at a dangerous speed when the vehicle hits the terminal itself. The barrier is designed to redirect the vehicle in a safer direction and impede its progress when the vehicle hits the barrier itself.
The terminals and barrier of the energy-absorbing guardrail are designed so that: (1) when the vehicle hits the barrier itself, the barrier is anchored by a cable or similar component with tensile strength to support the vehicle from moving excessively in a direction perpendicular to the roadway; and (2) when the vehicle hits the terminal, the cable or other support member is released to avoid pulling the barrier out of its alignment with the terminal which would prevent the movement of the terminal and barrier together to absorb energy.
A prior art guardrail of this class is described in U.S. Pat. Nos. 4,928,928 and 5,078,366 filed in the name of Sicking, et al. This prior art energy-absorbing guardrail has a terminal that extrudes a metal portion of the barrier, which is generally a W-beam rail or the like. In this prior art guardrail, the terminal, upon impact by a vehicle, moves along the rail, forcing the rail into a narrowing chute to extrude the rail and bend it into a roll, thus absorbing energy from metal working the rail. When the terminal is impacted, the cable anchoring the rail is released by the force of the impact.
This type of guardrail has several disadvantages, such as for example: (1) it is relatively expensive; and (2) the basic configuration cannot be readily adapted to different thicknesses of beam or to different materials from which the barrier may be constructed. Moreover, it is difficult to adapt the basic design to absorb energy at different rates depending on the nature of the roadway along which it is positioned. Thus, the rate of absorbing energy is the same for highways adapted to carry trucks and other vehicles at high speeds as it is for roadways having a lower speed limit and being adapted for smaller vehicles traveling at lower speeds although the highway may call for much more energy absorption per linear foot of travel of the vehicle striking the terminal.
Another prior art energy-absorbing guardrail of this class is disclosed in U.S. Pat. No. 4,655,434 to Bronstad and U.S. Pat. No. 4,838,523 to Walter P. Humble, et al. This prior art guardrail includes two parallel rails with horizontal connecting members between them. The terminal, when hit by a vehicle, moves along the guardrail, hitting the horizontal connecting members as it goes and causing the connecting members to move along a line of perforations in the metal rails, absorbing energy from the metal working as it moves.
This type of guardrail has a disadvantage of being expensive and not adapted for different sizes and speeds of automobiles without special design.
It is an object of the invention to provide a novel guardrail system.
It is a further object of the invention to provide a novel energy-absorbing terminal for guardrail systems.
It is a still further object of the invention to provide a method and apparatus for absorbing the energy of a vehicle that collides with a guardrail system.
It is a still further object of the invention to provide a method and apparatus for restraining and redirecting vehicles that collide with guardrail systems.
It is a still further object of the invention to provide a method and apparatus for making and using an energy-absorbing guardrail terminal adapted for a particular type of guardrail and an energy-absorbing guardrail terminal that can be inexpensively adapted for different types of guardrails.
It is a still further object of the invention to provide a method of making guardrails adapted for a particular highway and a guardrail which can be inexpensively adapted for the different highways.
It is a still further object of the invention to provide an energy-absorbing guardrail terminal useful with beams of reinforced plastic in a guardrail.
In accordance with the above and further objects of the invention, a guardrail system includes a guardrail and a guardrail terminal arranged so that the terminal cooperates with the guardrail to absorb energy if a vehicle hits the terminal and releases the guardrail upon impact of the vehicle with the terminal but anchors the guardrail if the guardrail is impacted by the vehicle instead of the terminal.
The terminal assembly includes an impact head and a cutting section. When the impact head is hit by a vehicle, it moves the cutting section in a manner to cut the beam of the guardrail and activates an anchor release to release the anchor from the guardrail itself. In the preferred embodiment, the guardrail is released from a cable by breaking the first post which has the cable bolted to it at one end. The other end of the cable is mounted to the guardrail. The post breaks at the cable connection, releasing the cable.
The cutting section includes a tube having one or more cutting members within it and a deflection plate. The cutting member or members are designed to aid the deflection plate in the absorption of energy.
For example, one or more shear type cutters may be located to reduce the moment of inertia of beams and thereby to reduce the total amount of energy absorbed per linear foot of travel for each portion of a beam when a thicker metal guardrail beam is used and thus compensate for the increased energy absorbed because of the thickness of the guardrail and vice versa. Thus, the guardrail system may be designed to accommodate different types and thicknesses of guardrail beams. Similarly, the energy absorbed for each linear foot of travel may be tailored for the nature of the traffic on the roadway such as to absorb more energy for roadways where the traffic is faster and includes heavier vehicles and to absorb less energy per linear foot for roadways in which the traffic is slower and includes lighter vehicles.
In the case of nonmetallic beams or beams of any other type that absorb energy during fragmenting by buckling, compression failure, breaking and tensile failure against or because of the deflecting plate rather than bending, such as some fiber reinforced plastic beams, cutters aid in centering the beam portions, in causing the fragmenting to take place near the deflection plate to increase the amount of energy to be absorbed and maintaining stability of the operation. For example, the proper angle of a wedge shaped cutter and the proper location of the cutter stabilizes the path of the fragments of the plastic reinforced beams after being cut. The shape and location of the cutters and the shape and location of the deflector plates affect the amount of fragmenting and thereby increase or decrease the energy absorption per foot of travel by increasing the fragmenting or decreasing the amount of fragmenting respectively.
From the above description, it can be understood that the guardrail system of this invention has several advantages, such as: (1) it is relatively inexpensive to fabricate; and (2) it may be easily designed for different rates of energy absorption without modifying the heavy frame structure and only modifying the cutting mechanisms themselves.